Transforming growth factor-beta (TGF-beta), is a negative regulator of epithelial cell growth via its ability to inhibit cell proliferation and/or induce apoptosis. The long term goal of the proposed studies is to determine whether deregulation of the TGF-beta signaling pathway, through which the biological signal is propagated, plays a significant role in initiation and progression of prostate cancer. We propose to use a human prostate tumorigenesis cell model system, the LNCaP cell line, in which specific loss of TGF-beta receptor type II function, is responsible for lack of responsivity to TGF-beta. In Specific Aim 1, the LNCaP prostate cancer cells will be transfected with a plasmid encoding the R-II gene, to establish the relationship between over expression of TGF-beta receptor II and the tumorigenic behavior of these cells. Results from these studies will indicate whether restoration of TGF-beta sensitivity in LNCaP cells by over expression of a functional R-II receptor, leads to reversion of malignancy. In Specific Aim 2 using R-II receptor overexpressing clones, we will investigate the potential downstream effectors that are essential for signaling/transducing the TGF-beta's antiproliferative and apoptotic effects. The expression of the cyclin-dependent kinase inhibitors, p21 WAF1/Cip1 and p27Kip1 and p16 will be examined in TGF-beta sensitive prostate cancer cells, after treatment with exogenous TGF- beta, by Northern and Western analysis, to determine whether deregulation of these potential effectors of the TGF-beta apoptotic signal occurs at a post-transcriptional or post-translational level. In Specific Aim3, PCR and genetic sequencing techniques will be used to screen for the occurrence of mutations in the R-II receptor gene, that affect the receptor structure and function in prostate cancer cell lines that are weakly sensitive to TGF-beta. Results from these studies will be critical in identifying whether a dysfunctional TGF-beta mechanism is of major significance in prostate cancer development and progression, via loss of expression or genetic alterations of its transmembrane receptors R-I and R-II genes and deregulation of the downstream effectors that transduce TGF-beta apopoptic signal.